/*
 * Copyright (C) 2009 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import java.util.Collections;
import java.util.List;
import java.util.ListIterator;

import javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Preconditions;

/**
 * Implementation of {@link ImmutableList} with exactly one element.
 * 
 * @author Hayward Chan
 */
@GwtCompatible(serializable = true)
@SuppressWarnings("serial")
// uses writeReplace(), not default serialization
final class SingletonImmutableList<E> extends ImmutableList<E> {
    final transient E element;

    SingletonImmutableList(E element) {
        this.element = checkNotNull(element);
    }

    public E get(int index) {
        Preconditions.checkElementIndex(index, 1);
        return element;
    }

    @Override
    public int indexOf(@Nullable Object object) {
        return element.equals(object) ? 0 : -1;
    }

    @Override
    public UnmodifiableIterator<E> iterator() {
        return Iterators.singletonIterator(element);
    }

    @Override
    public int lastIndexOf(@Nullable Object object) {
        return element.equals(object) ? 0 : -1;
    }

    public ListIterator<E> listIterator() {
        return listIterator(0);
    }

    public ListIterator<E> listIterator(final int start) {
        // suboptimal but not worth optimizing.
        return Collections.singletonList(element).listIterator(start);
    }

    public int size() {
        return 1;
    }

    @Override
    public ImmutableList<E> subList(int fromIndex, int toIndex) {
        Preconditions.checkPositionIndexes(fromIndex, toIndex, 1);
        return (fromIndex == toIndex) ? ImmutableList.<E> of() : this;
    }

    @Override
    public boolean contains(@Nullable Object object) {
        return element.equals(object);
    }

    @Override
    public boolean equals(Object object) {
        if (object == this) {
            return true;
        }
        if (object instanceof List) {
            List<?> that = (List<?>) object;
            return that.size() == 1 && element.equals(that.get(0));
        }
        return false;
    }

    @Override
    public int hashCode() {
        // not caching hash code since it could change if the element is mutable
        // in a way that modifies its hash code.
        return 31 + element.hashCode();
    }

    @Override
    public boolean isEmpty() {
        return false;
    }

    @Override
    public Object[] toArray() {
        return new Object[] { element };
    }

    @Override
    public <T> T[] toArray(T[] array) {
        if (array.length == 0) {
            array = ObjectArrays.newArray(array, 1);
        } else if (array.length > 1) {
            array[1] = null;
        }
        // Writes will produce ArrayStoreException when the toArray() doc
        // requires.
        Object[] objectArray = array;
        objectArray[0] = element;
        return array;
    }
}
